The invention relates to an apparatus and method for dewatering the suspension of comminuted fiber material and a liquid. There are many existing prior art structures for a suspension of comminuted fiber material and a liquid, such as shown in U.S. Pat. Nos. 3,579,420 and 3,348,390. While such prior art devices are generally successful, there usually is a passageway that is movable with respect to a container through which a suspension to be dewatered flows associated therewith. This means that there is a potential for leakage of fluid from the container, which leakage, of course, is undesirable. Also, such prior art devices are relatively complicated, and rely on an outside pressure source or the like for movement of a dewatering screen, while the present invention utilizes the liquid of the suspension, and/or liquid that is removed from the suspension, for movement of a relatively simple screen moving mechanism.
According to the present invention, a dewatering apparatus is provided which includes a generally circular cross-section container through which a suspension to be dewatered flows in a given direction, a hydraulic piston mounted substantially concentrically in the container and having an interior chamber therein for transporting liquid removed from the container to an area remote from the container (i.e., reservoir), screen means mounted on the piston for allowing the passage of liquid removed from the suspension through the interior chamber of the piston to the remote area, while not allowing removal of material suspended in the suspension therethrough, means responsive to the fluid pressure of liquid from the suspension for moving the hydraulic piston relative to the container in either a first direction, corresponding to the direction of flow of fluid in the container, or a second direction opposite to the first direction, the means including a first and a second piston faces, and means for forcing liquid removed from the suspension through the piston chamber to the second piston face to move the piston in the second direction, so that no substantially dewatering takes place during movement of the piston in the second direction and so that the piston is moved to a position wherein it again may be moved in the first direction. Preferably, means are provided to insure that the piston moves more quickly in the second direction than in the first direction, so that unclogging of the screen means is facilitated during movement of the screen means in the second direction. The screen means may comprise a plurality of annular screen members having an internal chamber thereof operatively connected to a plurality of supporting arms radially extending from the piston.
According to the method of dewatering of a suspension of comminuted fiber material in a liquid, according to the present invention, the following method steps are effected: a suspension to be dewatered is passed through a container in a first direction, and a portion of the liquid from the suspension is separated out with screen means, and the separated liquid is removed from the container. A piston supporting the screen means is moved in a first direction -- the direction of suspension flow -- under the pressure of liquid of the suspension while separating out of a portion of the liquid from the suspension takes place, and then the separating out of liquid from the suspension is substantially terminated while the piston is moved in a second direction, opposite to the first direction, under the influence of liquid which has been separated from the suspension. Preferably, backflushing of the screen means also takes place during movement of the piston in the second direction in order to further facilitate unclogging of the screen means.
It is the primary object of the present invention to provide improved apparatus and an improved method for dewatering of a suspension of comminuted fiber material and a liquid. This and other objects of the present invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.